1. Field of the Invention
This invention relates to the oligomerization of olefins and relates more particularly to a reproducible process for varying the degree of oligomerization of 1-olefins with boron trifluoride catalyst. Still more particularly, in one of its aspects, the invention relates to an improved process for the oligomerization of olefins, or olefin fractions, for the manufacture of synthetic fluid lubricants, employing alcohol-promoted or water-promoted boron trifluoride catalysts, or mixtures of such catalysts, under conditions in which the degree of oligomerization can be controlled in order to obtain olefin oligomers suitable for use as synthetic fluid lubricants for many industrial applications, particularly as low temperature hydraulic fluid.
2. Description of the Prior Art
It has been shown that oligomers of olefins having 6 to 12 carbon atoms may be hydrogenated to yield synthetic lubricants. See Hamilton and Seger U.S. Pat. No. 3,149,178. The preferred olefins are linear alpha olefins and the dimer is preferably removed to a major extent when necessary in order to provide lubricants of low pour point and high fire and flash points.
The catalysts employed for oligomerization are generally of the Friedel-Crafts type, activated by water or a primary aliphatic alcohol. Other activators include phosphoric acid as in U.S. Pat. No. 3,742,082. Boron fluoride is a catalyst suited to that purpose when so activated. It is recognized that boron fluoride is essentially inactive in the pure state, although such activity has been reported for polymerization of the extremely reactive olefin isobutylene. Even in that case, there is controversy whether the boron fluoride system is perfectly dry, it being postulated by some writers that traces of moisture on the apparatus employed may be sufficient for water activation of the catalyst. Certainly, for the less reactive olefins such as those used for manufacture of synthetic lubricants, useful degree of oligomerization is achieved only with boron fluoride to which has been added a minor measurable quantity of an activator such as water or a primary alcohol.
It is reported in Holmes U.S. Pat. No. 2,384,916 that polymerization of isobutylene at extremely low temperatures, e.g. -78.degree. C, in the presence of boron fluoride is promoted by certain oxygen-containing organic compounds, including low boiling esters. In accordance with Holmes teachings, the molecular weight of the product is increased in the range upwards of 100,000 by such promoter when the feed isobutylene is carefully freed from alcohol and the like by repeated distillations. See lines 67 to 71 of the first column on page 2.